The unexpectedly high percentage of aqueous extracts of marine organisms and terrestrial plants which exhibited AIDS-antiviral activity in the primary screen necessitated an investigation of recurring classes of antiviral agents and methods to differentiate such compounds from more unique anti-HIV compounds which might also be present. A series of simple experiments to test for known classes of AIDS-antiviral compounds, and to provide general chemical characterization of the anti-HIV compounds present, has been developed. The NCI in vitro primary antitumor screen, in conjunction with computerized pattern-recognition (e.g., Compare) algorithms, are also being explored as a dereplication approach for cytotoxic extracts.